Pulse transformer construction



March l1,` 1958 J. J. CAREY v PULSE TRANSFORMER CONSTRUCTION Filed Oct.'24. 1956 uvm United States Patent Office 2,826,747 Patented Mar. 11,1958 PULSE TRANSFORMER CONSTRUCTION James .1. Carey, Henrietta, YN. Y.,assignor to Dnion Coil $0., Inc., Caledonia, N. Y., a corporation of New'011k Application October `24, 1956, Serial No. 618,065

5 Claims. (Cl. 3136-1-92) This invention relates to electrical-transformers ,-and more particularly .to precision transformers of thetype used to ,generate transient pulses in Velectronic computingequipment and similar devices.

Miniature transformers of the type to which this invention relatesordinarily employ a 'toroidal ferrite core on which the primary landsecondary coils are wound.

These parts are enclosed in a housing or casing and the` connections tothe primary and secondary coils attached to lead wires carried to theoutside of the casing. The easing -is 'iilled with a potting compound.These elements are used in .large numbers in electronic assemblies whichare put together by automatic machinery. One of the problems encounteredis to ensure alignment of the lead wires so that they will be in ,properposition for automatic assembly operations. Hitherto it has beennecessary to straighten `and align the :lead wires after assembly of thetransformer in many cases. Furthermore, it is very important to ensureaccurate operation land long life of Yeach transformer element becausemany thousands of transformers are used in a computer, and failure ofany one will cause faultyperformance fof :the entire system. Detectionof the particular r,part which has failed is time consuming andexpensive. ln conventional transformers of this type, the core is heldin place in the casing merely by the potting compound with which thecasing is filled. The coils are of fine wire wound to very closetolerances to generate a pulse of specific shape. Consequently, minutemechanical strains are likely to cause a short circuit in the coils.

One of the objects of this invention is to facilitate proper alignmentof the lead wires of a miniature pulse transformer so that thetransformer can be readily as sembled with other circuit components byautomatic machinery. Another object is to ensure long life of thedelicate coil windings by permanently securing the core in the properposition and relieving the windings of mechanical strains arising fromshock, or expansion and contraction of the casing.

According to this invention, the annular or toroidal core, with theprimary and secondary windings, is iirst mounted in a hollow rectangularblock of moded plastic. Embedded in this block are tinned copper wireswhich are accurately bent to form studs for connection to the coilWinding wires and to form spaced parallelleads intended to extend fromeither end of the outer casing. The core is placed transversely throughthe block and a small piece of exible plastic tubing is forced betweenthe core and the block on either side to anchor the two together. Theblock fits closely enough inside a tubular casing to hold the core in apredetermined position, but has enough clearance to permit the leadwires to be aligned with bushings in glass plates which are used toclose the ends of the casing.

In the drawings illustrating the invention:

Fig. 1 is a plan view of a transformer constructed according to theinvention, the casing being shown in crosssection;

2 `Fig..2 is a side view of the core and shell assembly; land Fig. 3 isan -end view of the shell prior to assembly withthccore.

The .standard electrical elements of the transformer here shown are thetoroidal or ring-shaped .core 10, and the primary yand secondary'coils11 and 12. The block 13, shown before assembly in Fig. 3, is a hollow.rigid vrectangular piece preferably molded of thermosetting plastic,having a central .rectangular opening 13a, and pairs lof arcuate.notches 14 and 15 in Vits top vand `bottom walls 13b and 13e. Embeddedin the right-hand end wall 13d of the block are two lead wires 16 and 17made of tinned copper. These wires are :formed with long straightportions 16a, 17a, oblique oisets 16h, 17b,

and stud portions 16C, 17e which project upward and downward,respectively, through the block, the oblique v lportions being embeddedin the latter. The stud portions @may be .made accurately parallel, bymeans of a die,

rand spaced to line up with the bushings in the end plates. The `core10, with the coils 11 and v12 already wound Ion each yside in the-desired arrangement, vis slid into the opening 13 and apiece -of round,somewhat compressible `plastic tubingl-S .is inserted between one sideyof the .core and the-block at .notches .1-4. The core is then forcedover to the opposite side by compressing 'tube L8, and asecond jpiece'of compressible tubing 19 -is inserted lbetween Ythe opposite side ofthe core and block 13 at notches 15. When the core is released bothtubes are somewhat tlattened between the core :and the top and bottomwalls y'of the bloc-lt, and the core is centered in the block. The space`2i) in the interior of the vcore .is -then lled .resi-nso that the,core and block become firmly united. The coil wires are wrapped nnumber of times around studs 16e and 17c and soldered. The studs, alongwith any excess coil wire, are clipped off short after the coil wireshave been attached.

The core and block assembly fits into a tubular metal can 21 which has alining 21a of woven glass. The can has end grooves 2lb in which glassend plates 22 and 23, having metal rims 24 and 25, are seated. Theseplates have pairs of metal bushings 26 and 27 (only one being seen ineach case in Fig. 1) through which the leads 66 and 67 are passed andsoldered.

The preferred method of assembling the transformer in the casing is toset one end plate in place and solder its rim to the can. The block andcore assembly is then slid into the can, one pair of leads passingthrough the bushings of the attached end plate. The second end plate isthen slid along the other pair of leads into position, its rim issoldered to the can, and its bushings soldered to the respective leads.The assembled can is heated to drive out any moisture. Potting compoundis then owed into the can through the bushings of the first end plate.It is important to leave some space for thermal expansion of thecompound, as these transformers may be operated under temperatureconditions ranging from about 65 F. to 165 F. After the can has beenfilled to about the right degree, it is tilted and heated, causing anyexcess compound to leak out through the open pair of bushings. Thesebushings are then soldered to the respective leads.

It is understood that the coil windings may be varied in number andposition according to the electrical characteristics desired.

Pulse transformers of this type are made in very small sizes. Forexample, the casing may be about half an inch in diameter. In automaticassembly of various circuits, these parts are frequently rolled into afeeding mechanism. For this reason it is important that theprojectingleadrwires, Whichgmay be two or three inches long, be alignedwithin the diameter of the casing. The

embedding ofV thesewires into the plastic shell ensures their properplacement and alignment for this purpose, as

well as lining up the wires with the bushings. The Wire leads can besubsequently bent, cut, or otherwise manipulated without danger ofdamage to the coils, because any stress applied to the leads is carriedby the block. The rm anchoring of the core is important in prolongingthe life of the device, as the ycore ordinarily has square edges, andany relative movement between the core and the wire is likely to causethese edges to wear through the extremely thin insulation of the wires.

This transformer is relatively inexpensive to manufacture as the blockitself costs very little and results in,

core being disposed in said opening and having portions projectingtransversely outward therefrom to either side of said block; and twopairs of rigid lead wires, each pair having portions embedded in one ofsaid end walls and portions extending endwardly outward from the block,one wire of each pair having a stud portion projecting upward from saidtop wall and the other wire of each pair having a stud portionprojecting downward from said bottom wall, said coils having electricalconnections to said stud portions.

2. A transformer as described in claim 1, having a pair of compressiblemembers, one disposed between said block and each of the transverselyprojecting portions of said core.

3. A transformer as described in claim 2, said top and bottom wallshaving notches in which said compressible members are engaged.

4. A transformer comprising: a casing having end walls, each end wallhaving a pair of spaced bushings, a hollow block disposed in saidcasing; a first pair of rigid lead wires having portions embedded insaid block, stud portions extending from said block but contained withinsaid casing, and parallel lead portions aligned with and extendingoutward through the bushings of one of said end walls; a second pair ofrigid lead wires having portions embedded in said block, stud portionsextending from said block but contained within said casing, and parallellead portions aligned with and extending outward through the bushings ofthe other of said end walls; a transformer core mounted in said block;and primary and secondary coils wound on said core, each coil havingelectrical connections to two of said stud portions. l

5. A transformer comprising: a substantially toroidshaped core; primaryand secondary coils wound on said core; a hollow, generally rectangularinsulating block having a transverse opening and top and bottom walls,said core being disposed in said opening and having portions projectingtransversely outward therefrom to either side of said block; a pair ofcompressible members, one inserted between each of said projectingportions and said block, said top and bottom walls having aligned pairsof notches in which the respective compressible members are engaged; andrigid lead wires embedded in said block, said Wires having lead and studportions projecting from the block and said coils having electricalconnections to said stud portions.

References Cited in the le of this patent UNITED STATES PATENTS 506,577Adams Oct. 10, 1893 1,333,004 Vaughn Mar. 9, 1920 1,653,951 FeathersonDec. 27, 1927 2,098,070 Stimson Nov. 2, 1937

